Ed is the dedicated, longtime chief of police on Nantucket Island. Having recently survived a massive heart attack, he plans to retire at the end of the summer but finds himself drawn into one last major investigation. He is deeply embedded in the local community and is a core member of a close-knit friend group known as the Castaways.

Leslee is a flamboyant, socially aggressive newcomer to Nantucket who attempts to buy her way into the island's elite circles. She hosts extravagant events at her compromised waterfront home, Triple Eight, and intensely pursues membership at the exclusive Field and Oar Club. Her disregard for boundaries and highly inappropriate behavior quickly create friction with the established locals.

Bull is a wealthy Australian businessman who owns a beverage-distribution company and occasionally produces films. He indulges his wife Leslee's extravagant tastes and social climbing while trying to manage his own mounting business challenges. Despite his immense wealth, his business practices draw scrutiny from regulatory agencies.

Coco is a young, aspiring screenwriter from Arkansas who moves to Nantucket to work as the Richardsons' personal concierge. Hoping to use Bull's industry connections to advance her script, she instead finds herself running endless errands and managing the couple's chaotic demands. Her sudden disappearance after a fire at their estate drives the present-day investigation.

Kacy is Ed and Andrea's daughter, a neonatal intensive care nurse taking a summer leave from her job in San Francisco. She returns to Nantucket seeking clarity regarding her complicated romance with an engaged colleague. She quickly befriends Coco, acting as her guide to the island's social structures.

Andrea is Ed's supportive wife and a foundational member of the Castaways friend group. She hosts dinners and provides a stabilizing presence for her family and friends as they react to the disruptions caused by the Richardsons' arrival.

Phoebe is a wealthy, established Nantucketer and a key member of the Field and Oar Club's membership committee. As part of the Castaways, her long-standing friendships are tested when Leslee targets her as a means of gaining entry into the island's most exclusive social circles.

Delilah is a passionate member of the Castaways who has spent nine years trying unsuccessfully to gain entry into the Field and Oar Club. She grows increasingly resentful of Leslee's aggressive social climbing and feels deeply threatened by Phoebe's growing association with the newcomer.

Addison is Phoebe's husband and a successful local realtor who facilitated the Richardsons' purchase of their home, Triple Eight. He attempts to leverage this connection into a lucrative real estate development deal with Bull, only to discover his client's unreliable business ethics.

Lamont is a handsome, highly skilled sailor from an established Cape Verdean family on Nantucket. He returns home to care for his mother and accepts a well-paying job captaining the Richardsons' yacht. He soon finds himself caught between his employers' strict non-fraternization rules and his growing attraction to Coco.

Known locally as the switchboard operator of the island's rumor mill, Sharon spends her summer taking a creative writing class and attempting to rebuild her life after her husband leaves her for a younger woman. She closely tracks the movements of the Richardsons while experiencing her own unexpected romance.

Eddie is a prominent local real estate agent who partners with Addison on speculative housing developments. He attempts to secure Bull as a major investor but grows wary when Bull insists on cutting corners with off-island contractors.

Zara is the incoming police chief set to replace Ed upon his retirement. She partners with him to investigate the fire and the sudden disappearance of the Richardsons' concierge, valuing his local expertise.

Romeo is a working-class employee on the island who strikes up a genuine connection with Sharon. He faces judgment from the island's wealthier residents but remains entirely unfazed by their elitism.

Eric is Ed and Andrea's son. He spends his summer enjoying the island with his girlfriend Avalon while actively avoiding the Richardsons after Leslee makes inappropriate advances toward Avalon.

Avalon is Eric's girlfriend and works as a masseuse on the island. She actively avoids Leslee after facing a highly uncomfortable and inappropriate proposition during a professional session.

Isla is a head neonatologist in San Francisco who maintains a secret, complicated relationship with Kacy. Her inability to break off her engagement causes Kacy to seek distance on Nantucket.

Jeffrey is Delilah's husband. He largely stays out of the social warfare his wife wages regarding the Field and Oar Club, though he supports her as part of their long-standing friend group.

Benton is a local landscaper tasked with executing Leslee's extravagant design visions. He frequently finds himself dodging Leslee's inappropriate physical advances while trying to secure payment for his work.

Busy is the commodore of the Field and Oar Club and represents the old-money establishment of Nantucket. She acts as a gatekeeper to the island's elite spaces and holds classist views toward working-class residents.